On Thu, Dec 01, 2016 at 10:15:04AM +0800, Dennis Chen wrote:
> The __pci_enable_msi_range() should return -ENOSPC instead of -EINVAL
> when the device doesn't have enough vectors as required, just as the
> MSI-X vector allocator does in __pci_enable_msix_range(). Otherwise,
> some drivers depending on that return value will probably fallback to
> the legacy interrupt directly, for example, in commit 17a51f12cfbd2814
> ("ahci: only try to use multi-MSI mode if there is more than 1 port"), the
> ahci driver will fallback to single MSI mode only when the return value
> is -ENOSPC in case of required vectors is not enough, else the driver will
> use legacy interrupt which has been observed on a x86 box with 6-port SATA
> controller.
Unless Christoph objects, I'll apply this, but I don't understand the
situation with 17a51f12cfbd. That commit doesn't check for EINVAL or
ENOSPC so I don't know what the connection with this patch is.
I know Christoph said he changed something in ahci to treat all errors
the same, but I don't know where that is, either.
If there's a revision of Linus' tree that is broken, please give the
details so I can at least describe which versions are broken, when it
got fixed by Christoph, and figure out whether we need stable
backports or anything.
Bjorn
> With this patch, when a MSI-capable device doesn't have enough MSI
> vectors as requested, it will fallback to single MSI mode while not
> legacy interrupt.
>
> Signed-off-by: Dennis Chen <dennis.chen@xxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Tom Long Nguyen <tom.l.nguyen@xxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> Cc: Steve Capper <steve.capper@xxxxxxx>
> Cc: linux-ide@xxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> ---
> drivers/pci/msi.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index ad70507..da37113 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -1084,7 +1084,7 @@ static int __pci_enable_msi_range(struct pci_dev *dev, int minvec, int maxvec,
> if (nvec < 0)
> return nvec;
> if (nvec < minvec)
> - return -EINVAL;
> + return -ENOSPC;
>
> if (nvec > maxvec)
> nvec = maxvec;
> --
> 2.7.4
>
>
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